he Palm cradle
looks pretty slick and comes with a switching regulator power supply.
It is however not an ideal lithium battery charger. See below.

This
article examines how Palm intended to charge the Palm Vx internal lithium
cells. The cradle was put to test in the following circuit.

The
test circuit

The test circuit
uses a variable power supply (V1) with a shunt resistor (R2). This way
the cell voltage can be more easily simulated and measured nicely in
0.05V increments. Series resistor R1 is used to measure the load current.
It is made 1 ohm because I think the Palm lithium cell also has roughly
the same internal resistance. This is based on a small cell voltage
drop (3.85V to 3.83V according to the palm) when removing a small load
current (25mA).
R3 has been added to make sure the cradle detects the connected circuit.
The styus holder light will lite. As for the measurement results, it
hardly made a difference whether this was connected or not.

The
test results

The measurements
show clearly that the cradle is not a constant current charger. It actually
looks like a 4.04V voltage source with an internal resistance of 1 ohm.
From the image can be derived there is a 2 ohm series resistance, but
that includes the 1 ohm in our test load circuit.

The charger seems
to deliver a hefty 150mA at the Palm battery-low warning level of 3.75V.
I have no knowledge of the actual capacity and optimal charge current
of the Palm lithium cell yet, but this could be on the high side of
what is considered healthy. Probably it is better for the lifetime your
cells to recharge them regularly when not really empty, then to wait
until you get a warning. Remember that lihium cells do not suffer from
a memory effect as NiCad cells do.

As the cells become
more full, the charge current reduces. This is the reason why it takes
much longer to get from 70% to 100% charge then it is from 40% to 70%.